Cell is the structural and functional unit of life.
It is a bit of protoplasm surrounded by a membrane.It is
formed from pre existing cells. Protoplasm is a gel like
material present inner to the cell membrane. Purkinje discovered
protoplasm. Protoplasm is the physical basis of life. The
jelly like material present inner to the cell membrane and
outer to the nuclear membrane is called cytoplasm. It contains
cell organelles. These cell organelles carry out all the
activities of the cell and all these activities are controlled
by the nucleus. Gel like material present inside the nucleus
which contains chromosomes is called nucleoplasm. Chromosomes
in the nucleus controls all the activities of the cell.
They are made up of genes. Nucleoplasm is denser than cytoplasm
but there are some organelles which fix in the nucleus in
the proper position thus making it float on the cytoplasm.
It is the endoplasmic reticulum which makes nucleus stable.
Cell is formed of pre existing cells. This theory is called
'Omnis Cellula Cellulae'. Total functioning of the cell
is controlled by each and every cell. Animal cell lacks
cell wall, vacuoles and chloroplasts. Vacuoles are very
small and reconsidered absent.
Plant cell lack centrosomes. They help in cell division.
In plants centrioles are directly formed without any chromosome
and they control cell division. The rigid shape of a plant
cell is due to the cell wall which is made up of cellulose.
Cell wall is dead, provides protection and is freely permeable
(it allows the easy passage of material).There are holes
present on it. Cellulose is a type of carbohydrate made
up of glucose. We cannot digest cellulose. The carbohydrate
which we can digest is called starch.
Cell membrane is also called plasma membrane. It is present
inner to the cell wall. In plant cell inner to the cell
wall the protoplasm is covered by cell membrane or plasma
membrane. In animal cell the cell membrane is the outermost
covering. Cell membrane protects protoplasm. It is selectively
permeable i.e., it will select the material which can be
transported across the membrane.
Cytoplasm is present between nucleus and the plasma membrane.
Its main component is water. It also contains some dissolved
materials. Matrix is composed of water, some dissolved and
some suspended material. It contains cell organelles.
Endoplasmic reticulum is a network of membranes connecting
cell membrane and nuclear membrane. On its surface ribosomes
may be present, then it is called rough endoplasmic reticulum
if not present then it is called smooth endoplasmic reticulum.
It acts as the cytoskeleton of the cell. It gives the cell
the required shape. Intra-cellular transportation of material
is carried out by it. It also stores fats, proteins and
carbohydrates. Thousands of ribosomes are present in the
cell. They are formed of smaller sub-units.they are granular
and are not enclosed by any membrane. The function of ribosomes
is to produce proteins. RNA determines the number of proteins.
Mitochondria are double membrane bound organelles called
'power house of the cell'. In the inner membrane there are
several foldings or invaginations called cristae. All over
this membrane oxysomes are present cristae increases surface
area for more oxysomes. Oxysomes controls cellular respiration
which produces ATP. It functions mainly as a compartment
for aerobic respiration and ATP synthesis. It produces and
stores energy. ATP (adenosine triphosphate) provides energy
for all life activies.
Golgi complex consists of three structures. Cisternae are
plate like structures present one over another. Vesicles
are rounded or oval structures. Tubules are irregular shaped
structures. Their main function is secretion and storage
of carbohydrate, proteins and fats. Hydrolytic enzymes are
present in lysosomes.These enzymes can digest the whole
cell when the body is in severe starvation. They are also
called suicidal bags of the cell. They protect the cell
from any other organism which enters the cell. They carry
out digestion of materials. If any complex material enters
the cell then lysosomes convert it into simpler material
and make it fit for use by the cell.
Centrosomes are present only in animals. Two centrioles
are present inside the centrosome. Centrosome is present
just outside the nucleus. It controls cell division and
the genes are also controlled by centrosomes.
Plastids are present only in plant cells. They are of 3
types - chromoplasts (gives colours to the plant except
green), leucoplasts(colorless plastid it stores food material)
and chloroplasts (green coloured plastid). Their function
is to perform photosynthesis. Chloroplasts are surrounded
by two membranes. Inner to the inner membrane stroma is
present. It contains several membrane plate like structures
called thylakoid. They are arranged one over another to
form grana. Thylakoid of the adjacent grana are connected
by frets or lamella.
Nucleus is covered by two membranes and in between there
are openings called nucleopore for the exchange of material.Inner
to this membrane matrix is present which is called nucleoplasm.
Inside the matrix thread like structures are present which
are called chromatin or chromatin fibers. It contains genes
to determine various characters to the organism. Chromatin
are made up of DNA ( de-oxy ribonucleic acid) which controls
all the characters of the organism. The pat of the DNA which
is responsible of the production of one character is called
gene. Like this several genes are present in several chromatin
or DNA's. Chromatin are loose but they attain a definite
shape by coiling this is called chromosomes. Two sets of
chromosomes are present ,total 46, in which 23 are of father
and 23 are of the mother.Chromosome is a hereditary material
it goes from father or mother to the offspring.
Cell inclusions are dissolved or suspended in the cytoplasm.
Carbohydrates are dissolved in different forms. Some of
the carbohydrate are insoluble while some are insoluble.
Carbohydrate forms a crystal like appearance called starch
grains. Proteins form a crystal like appearance called aluerone
layer. Fat is present in the form of fat globules. It is
a reserved fat material present in the cytoplasm. We classify
inclusions into 3 categories - reserved products, secretory
and waste products. In case of banyan tree cystolith are
present they are actually calcium carbonate crystals due
to the excess of material. They are present lower surface
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